The present invention concerns a method of determining a physical property of a liquid sample to include a viscometric and/or Theological property if not a structural physical property such as gelation and/or crystallization, which employs a rotating viscometer, especially a Scanning Brookfield Viscometer technique which employs a Brookfield-type head having a high torque capacity; as well as a device useful for carrying out the same, which is the Brookfield-type head having the high torque capacity in combination with temperature-scanning equipment. In essence, the invention provides ways and means to measure low and/or high temperature viscosity of a liquid, for example, a motor oil having a very high viscosity and/or a gelation point owing to its intrinsic properties, oxidation and/or sooting and so on, with an accuracy, precision, rapidity, and repeatability heretofore unknown in the art, as well as provide data heretofore inaccessible or unknown in the art, by employment of a temperature-scanning technique.
I. In General
Standard Scanning Brookfield techniques are well known in the field of viscometry and rheology. See, e.g., ASTM D 5133-96. In general, the standard Scanning Brookfield technique (SBT) is a method in viscometric testing for determining certain characteristics and parameters of fluids, for example, engine oils. Many of the standard runs vary the temperature from zero to minus forty degrees C, with small incremental changes in temperature over two to three days. Some, however, expand the temperature range, say, from +25 to xe2x88x9270 degrees C. See, Savant, Inc., Lubrication Technology, May, 1998, pages 1, 2 and 4. Note, Selby et al., U.S. patent application Ser. No. 09/032,661 (abandoned) which discloses how the jet fuels and the like low viscosity liquids can be analyzed. In the standard techniques, however, very high viscosity liquids are found to be poor candidates for the techniques, if they can be considered to be effectively characterized at all. In fact, the ASTM D 5133 method cannot provide all data necessary for engine lubrication fluids under all operating conditions. For example, in internal combustion engine operation, fluid operation characteristics concerning the region of fluid operation in the so-called xe2x80x9cThird Zone,xe2x80x9d i.e., from the pump to the lubrication site, are being recognized as a critical area of concern in lubricant performance.
Nevertheless, in the ever more sophisticated art of lubricant characterization and employment, very high viscosity liquids come more and more under consideration. High viscosity and gelation of lubricating oil, for example, can be of critical concern not only when exposed to very low temperature environments but also in higher temperature environments when the engine oil is highly loaded with engine soot, when the engine oil is highly oxidized, or both. And yet, efficient test methodology is lacking in this critical area, which can be employed to predict lubrication fluid performancexe2x80x94before engine breakdown may occur as a result of the use of an inadequate lubricant.
Actually, engine oils which show classic gelation in sensitive bench test devices developed to correlate with field-failing oils show little or no evidence of gelation effects in fairly recent ASTM cold-room pumpability work. In addition to raising questions about the meaning of the pumpability results, this has led to difficulty in developing correlations between results from the engines and the bench-test sources of low-temperature data.
Brookfield-type rotational viscometer heads having low, medium, high and very high sensitivities are known. See, TABLE 1, infra. The medium, high and very high sensitivity models, in particular, are heretofore known to be employed in set, single-temperature settings, and data and correlations obtained therefrom are limited.
II. Brief History
Pumpability of engine oils at low temperatures has been an ongoing concern for a number of years, particularly for engine manufacturers who have seen pumpability problems as increasing their burden of warranty costs. See, Appeldoorn, xe2x80x9cMotor Oil Viscosity and Cold Starting,xe2x80x9d API Mtg., Chicago, November, 1948; SAE PT-10, pp. 1-6; Selby, xe2x80x9cViscosity and the Cranking Resistance of Engine Oils at Low Temperatures,xe2x80x9d 6th World Petroleum Congress Proceedings, Section VI, Frankfurt, June, 1963, pp. 241-258; McMillan et al., xe2x80x9cThe Relationship of Low-Temperature Rheology to Engine Oil Pumpability,xe2x80x9d SAE Paper No. 730478 (SP-382), Viscosity and Its Application to Automotive Lubricants, SAE National Automobile Engineering Meeting, Detroit, May 14-18, 1973; Groh, xe2x80x9cPumpabilityxe2x80x94Tempus Fugit,xe2x80x9d Proceedings of the 1982 International Conference on the Viscometry of Automotive Lubricants, pp. 57-64, published 1983 by Savant, Inc., and Bierylo, xe2x80x9cLow-Temperature Deficiencies in Marketed Engine Oils,xe2x80x9d Proceedings of the 1982 International Conference on the Viscometry of Automotive Lubricants, pp. 65-68, published 1983 by Savant, Inc. While either the engine oil or the engine design (or a combination of both) may be the primary cause, the extensive damage that can ensue from a lack of sufficient oil supply to highly loaded lubrication sites in the engine often obscures any role of the oil. Oil-induced pumpability failure thus places warranty costs on the engine manufacturer unless there is an epidemic of failures identifying a common oil linkage.
An emphasis has been placed on lower SAE W-Graded engine oils
For several years engine manufacturers have encouraged the use of lower viscosity, multi-grade engine oils such as SAE 5W30 and 10W30. Reasons given have been a quicker supply of oil to lubrication sites at low temperature as well as fuel efficiency benefits. This direction of technical development would seem to also improve rapidity of lubricant flow in the engine on start-up at low temperatures.
Highly refined, hydro-treated base stocks have aided such development but also brought about the need to treat the increased paraffinic content of these highly refined mineral oil base stocks carefully with pour-point depressants. Such oils can be very sensitive to type and concentration of the pour-point depressant and thus require careful monitoring in production to avoid misblends having significant gelation. See, Kinker et al., xe2x80x9cEvaluation of the Low Temperature Performance of Engine Lubricants Using the Scanning Brookfield Viscometer,xe2x80x9d 11th International Colloquium on Tribology, Stuttgart, Jan. 13-15, 1998.
Additionally, it has been shown that even mixing brands of engine oils can produce gelation as a result of the interaction of viscosity index (VI) Improvers in one lubricant with the pour-point depressant and paraffinic content of another oil. See, Rhodes, xe2x80x9cLow-Temperature Compatibility of Engine Lubricants and the Risk of Engine Pumpability Failure,xe2x80x9d SAE Paper No. 932831 (SP-996), SAE Fuels and Lubricants International Fall Conference, Philadelphia, Oct. 18-20, 1993; Rhodes, xe2x80x9cAssessment of the Low-Temperature Incompatibility Risk of Commercial Engine Oils,xe2x80x9d SAE Paper No. 941976 (SP-1055), SAE 1994 Transactions, Journal of Fuels and Lubricants, Section 4, pp. 1342-1351.
III. Heretofore Known Status of Pumpability Studies
At low ambient temperatures, the importance of rapidly supplying engine oil to lubrication sites in the engine has led to incorporating pumpability limits in SAE J300 as well as the establishment of firm specifications by automotive engine manufacturers limiting the level of engine oil gelation as measured by the so-called Gelation Index. These specifications have been applied to engine oils used both internally (factory fill) and internationally. See, Ford Motor Co., Inc., Ford Engineering Material Specification WSB-M1C241-A, 1993; Chrysler Corp., Engineering Standard No. MS-9767, June, 1995; Cummins Engine Co., Inc., Material Specification No. 20,057-00, May, 1985; Engine Oil Licensing and Certification System, xe2x80x9cILSAC GF-2 Minimum Performance Standard for Passenger Car Engine Oils,xe2x80x9d Nov. 6, 1995.
More critically for the engine manufacturer is the possibility that borderline pumpability conditions may result in progressive damage to engine components which only show up as abbreviated engine life. With today""s 100,000-mile extended warranties for the consumer, this again translates to higher warranty costsxe2x80x94albeit at higher mileages.
As just mentioned, an epidemic of failures in a short period of time at a given location brings attention to the role of the engine oil. This was the situation in Sioux Falls, S.D., several years ago, and is known as xe2x80x9cThe Sioux Falls Incident.xe2x80x9d
During the winter of 1980-1981, a certain weather condition produced an oil rheology in at least one brand of oil causing failure in a number of engines. Even in this case, the cause triggering the failures was not clearly identified until careful research in cold-room engine studies revealed that the engine oil would, under certain cooling conditions, become highly gelated. See, Stambaugh et al., xe2x80x9cLow Temperature Flow Properties of Engine Oils,xe2x80x9d SAE Paper No. 820509, SAE International Congress and Exposition, Detroit, Feb. 22-26, 1982.
On starting the engine, this produced a condition called xe2x80x98air-bindingxe2x80x99 (cf. FIG. 1) in which the oil pump pulls a vortex of air from the oil surface.
Since that time, the nature of pumpability failure and pumpability testsxe2x80x94both on the laboratory bench and in cold-room enginesxe2x80x94have been a major focus of study, discussion, and specification development. See, Stewart et al., xe2x80x9cThe Relationship Between Oil Viscosity and Engine Performancexe2x80x94A Literature Search,xe2x80x9d SAE Paper No. 770372 (SP-416), in Stewart et al. (Eds.), The Relationship Between Engine Oil Viscosity and Engine Performance, SAE, 1977, pp. 1-19.
Advances in startability have an impact on pumpability.
More recently, as a result of advances in easing engine startability at low temperatures, pumpability has emerged as the most critical low-temperature lubrication problem. See, Selby, xe2x80x9cProblems in Bench Test Prediction of Engine Oil Performance at Low Temperature,xe2x80x9d SAE Paper No. 922287 (SP-986), SAE International Fuels and Lubricants Meeting and Exposition, San Francisco, Oct. 19-22, 1992. With higher horsepower generated in smaller engines, the need to rapidly get lubricant to the critical lubrication sites before wearing conditions intensify is even more criticalxe2x80x94particularly at low temperatures when the oil is most viscous and resistant to flow.
The question of pumpability in modem engines has been renewed.
In 1992, with no significant evidence of pumpability problems for a decade, questions were raised regarding the continued need for, relevance of, and startability relationship with, pumpability and gelation. Subsequently, a letter was written by the Chairman of the SAE Fuels and Lubricants Committee to the appropriate level of ASTM Committee D-2 requesting that the subjects of pumpability, startability, their interrelationship, and their instrument dependence be revisited. Note, Sheahan, Letter to Messrs. Houubec and Duffy, May 29, 1992, which discusses evolution of low-temperature viscosity requirements in the Engine Oil Viscosity Classification SAE J300, and requests ASTM to conduct a low-temperature study of the cranking, starting, and pumping requirements of modern engines.
The xe2x80x98if start, must pumpxe2x80x99 concern is an important concern, which is to assure that an oil""s pumpability would be sufficient to satisfy the lubrication needs of a modern engine after it was started and running at low ambient temperatures. With fuel injection and electronic ignition, these engines were capable of starting at considerably lower temperatures and higher viscosities than in the early 1960s. Partially because of one difficult-to-start engine as reported by Selby, xe2x80x9cA Comparison of the Effects of Cranking Speed and Oil Viscosity on Low-Temperature Engine Starting,xe2x80x9d SAE Paper No. 640427 (805C), SAE Automotive Engineering Congress, Detroit, January, 1964 (but also because of results of a number of other studies as reported in the SAE Paper No. 770372), 3500 centipoise (cP) had been established as a maximum low-temperature viscosity for the most widely used SAE multi-grade engine oils (i.e., those carrying 5W-, 10W-, or 15W-xe2x80x98Xxe2x80x99 as part of their SAE viscosity classification).
The ASTM response to the SAE request was to immediately conduct an ASTM starting and pumping study through formation of a Low-Temperature Engine Pumpability (LTEP) Task Force under Subcommittee 7 of ASTM Committee D-2. This task force had the responsibility of meeting the SAE request by conducting relevant cold-room starting and pumpability studies with modern engines and correlating the latter with the bench instruments being used.
A number of automotive, petroleum, and additive engineers and scientists joined this Task Forcexe2x80x94several of whom had served on the first Pumpability Task Force of the 1970s.
Three needs were evident once cold-room facilities were selected. These needs were identified as follows:
1. choose appropriate test engines;
2. develop cold-room techniques emulating what nature might do to produce field gelation conditions in the sump; and
3. obtain or make engine oils which would have a suitable range of gelating tendency (air-binding response). (The other form of pumpability failure through viscous pumping difficulties, or xe2x80x98flow-limitedxe2x80x99 behavior, could be readily induced without special cooling techniques.)
Startability issues were addressed. Startability study protocols were relatively easily established and reasonably straightforwardxe2x80x94cooling time, temperatures of test, cranking duration, frequency of attempted restart, battery condition, test data to be gathered, etc., were the primary factors and issues considered.
Pumpability issues were considered. Pumpability issues, on the other hand, required much more thought and discussion. Test protocols were needed that might be successful in producing gelation in the cold-room with the hope of anticipating and imitating low-temperature weather anomalies in nature.
Bench test correlation issues were assessed. As previously noted, a further part of the request by the SAE was to assess the bench tests used in pumpability measurements to determine how they correlated with pumpability failures in engines. A basic question was raised during early discussions whether to first prove an engine test protocol that would display air-binding or to try three or four protocols on several test oils and to accept the engine response whether or not air-binding was displayed. The latter path, which was decided upon, was less time-consuming and costly but, if air-binding were not shown in the cold-room tests, also less persuasive as being imitative of nature.
IV. Background in Bench Tests
The MRV and ASTM D 3829 methods were developed.
One of the primary reasons for care and concern in developing pumpability tests by the LTEP Task Force was the memory of the prior ASTM cold-room engine pumpability studies in the 1970s. The information from these earlier cold-room pumpability tests was used to develop an instrument capable of showing good correlation with those same engine pumpability tests. This instrument was called the Mini-Rotary Viscometer (MRV) and was accepted as the ASTM Test Method D 3829 in 1979. See, Low-Temperature Pumpability Characteristics of Engine Oils in Full-Scale Engines, ASTM Data Series DS 57, Data Analysis Panel, RDD 7C, Ed., ASTM, 1995; H. Schaub, M. F. Smith, and C. K. Murphy, xe2x80x9cPredicting Low Temperature Engine Oil Pumpability with the Mini-Rotary Viscometer,xe2x80x9d SAE Paper No. 790732, SAE Passenger Car Meeting, Dearborn, Mich., Jun. 11-15, 1979; H. Schaub and C. K. Murphy, xe2x80x9cMini-Rotary Viscometer and Engine Oil Pumpability,xe2x80x9d STLE 35th Annual Meeting, Anaheim, Calif., May 5-8, 1980; ASTM Standard Test Method D 3829-93, xe2x80x9cPredicting the Border-Line Pumping Temperature of Engine Oil,xe2x80x9d 1998 Annual Book of ASTM Standards, Section 5, Vol. 05.02, ASTM, 1998, pp. 595-599.
The Sioux Falls Incident had an impact.
The cold-room engine tests of the first ASTM pumpability study were as well-conceived and engineered as the limited pumpability knowledge of that time would permit. However, as happens all too frequently in efforts to anticipate the vagaries of nature, the conclusions from this earlier study were swept aside by the later episode of engine failures in Sioux Falls caused by a set of weather conditions producing air-binding response mentioned earlier. This failing condition of the oils was not indicated by Method D 3829.
In retrospect, it was recognized that the cold-room engine pumpability test protocols used were only a part of a much larger population of possible test protocolsxe2x80x94any number of which might be reasonably encountered in nature.
Efforts were made to develop correlative instruments.
The availability of field-failing engine oils was an opportunity to develop new approaches to the bench measurement of pumpability-related oil rheology.
In 1981, a different form of bench test was developed, the SBT. See, Selby, xe2x80x9cA discussion of a paper by R. L. Stambaugh and J. H. O""Mara, Rohm and Haas Co., entitled: xe2x80x98Low Temperature Flow Properties of Engine Oils,xe2x80x99 given at the 1982 SAE International Congress, Feburary 22-26,xe2x80x9d published as Annex 4 to ASTM Research Report No. D02-1261 for the Scanning Brookfield Technique, Approved by ASTM, Oct. 26, 1990. The test was shown to be gelation-sensitive, and was later shown capable of direct measure of gelation intensity by calculation of the Gelation Index, a method of measuring the strength and extent of gelation. See, Selby, xe2x80x9cThe Scanning Brookfield Technique of Low-Temperature, Low-Shear Rheologyxe2x80x94Its Inception, Development, and Applications,xe2x80x9d in Rhodes (Ed.), Low-Temperature Lubricant Rheology Measurement and Relevance to Engine Operation, ASTM STP 1143, ASTM Committee D-2, Subcommittee 7, Lubricant Flow Properties, Austin, Dec. 10, 1991; Selby, xe2x80x9cFurther Considerations of Low-Temperature, Low-Shear Rheology Related to Engine Oil Pumpabilityxe2x80x94Information from the Scanning Brookfield Technique,xe2x80x9d SAE Paper No. 852115, SAE International Fuels and Lubricants Meeting and Exposition, Toronto, Nov. 2-5, 1985; Selby, xe2x80x9cThe Use of the Scanning Brookfield Technique to Study the Critical Degree of Gelation of Lubricants at Low Temperature,xe2x80x9d SAE Paper No. 910746, SAE International Congress and Exposition, Detroit, Feb. 25-Mar. 1, 1991; ASTM D 5133-96. This SBT protocol required a 1xc2x0 C./hour continuous scan of the oil""s viscosity over the low temperature range likely to be encountered.
Regarding the MRV, strong efforts were made to revise its test protocol over the five years following The Sioux Falls Incident. After the dedicated efforts of several investigators, in 1987 a revised MRV technique, code-named TP-1, was established. Note, Stewart et al., xe2x80x9cSummary of ASTM Activities on Low Temperature Engine Oil Pumpability,xe2x80x9d SAE Paper No. 821206, SAE Fuels and Lubricants Meeting, Toronto, Oct. 18-21, 1982; Smith, Jr., xe2x80x9cBetter Prediction of Engine Oil Pumpability Through a More Effective MRV Cooling Cycle,xe2x80x9d SAE Paper No. 831714, SAE Fuels and Lubricants Meeting, San Francisco, Oct. 31-Nov. 3, 1983; Henderson, xe2x80x9cMini-Rotary Viscometer TP-1 Cooling Profile Review,xe2x80x9d oral presentation handout, 1984 International on the Viscometry of Automotive Lubricants, Gaylord, October 1984; Henderson et al., xe2x80x9cNew Mini-Rotary Viscometer Temperature Profiles That Predict Engine Oil Pumpability,xe2x80x9d SAE Paper No. 850443 (3116R), SAE International Congress and Exposition, Detroit, Feb. 25-Mar. 1, 1985; ASTM D 4684-97. In contrast to the SBT, the MRV cools the sample quiescently and, thus, produces one value per test at the temperature of interest.
Both instruments require extended coolingxe2x80x9425 hours from xe2x88x925xc2x0 to xe2x88x9230xc2x0 C. for the SBT; 46 hours from xe2x88x925xc2x0 to xe2x88x9230xc2x0 C. for the MRV.
V. New Pumpability Challenges
Recent developments regarding passenger car engine oil were made. The combination of highly paraffinic base oils, need for careful selection of pour-point depressants, and the influence of the other additives has placed a premium on good pumpability of the oil and the additional impact of other additive chemistry introduced when the crankcase is topped up with a different engine oil. The latter factor was studied and reported in papers by Rhodes in 1993 and 1994. Note, the SAE Paper Nos. 932831 and No. 941976.
Essentially, it appears that with the development of more highly paraffinic base oils, the careful balance of the base oil, the pour-point depressant, the VI Improver, and the additive package must not only be obtained for the fresh oil but maintained in the used oil during its life in the engine. This of course brings in the effects of base stock and additive exposure to oxidation and, extending the above observations by Rhodes, the potential impact of oil admixtures between drain intervals. In turn, these effects must be coupled with the degree of oxidation and viscosity increase imposed by longer drain intervals.
Recent developments regarding heavy duty diesel engine oil were made. Another impact on low-temperature pumpability has been encountered recently in the area of heavy duty diesel engines. Note, McGeehan et al., xe2x80x9cThe Pivotal Role of Crankcase Oil in Preventing Soot Wear and Extending Filter Life in Low Emission Diesel Engines,xe2x80x9d SAE Paper No. 1999-01-1525, International Spring Fuels and Lubricants Meeting and Exposition, Dearborn, May 3-6, 1999.
Government requirements for major reduction in the emission of oxides of nitrogen from these engines has resulted in retarding the combustion cycle with the result that large quantities of soot are generated. This soot rapidly loads the engine oil to levels of 10% and higher. The effect of such high soot loading on the action of dispersant additives and the strong possibility that lack of control of such soot levels could adversely affect pumpability even at higher ambient temperatures is a serious concern.
VI. Desires and Needs in the Art
It would be desirable for effective lubrication to be able to provide adequate lubrication and freedom from oil gelation. Moreover, in line with the same, it would be desirable to be able to ascertain under laboratory conditions those lubricants which are so effective.
The present invention provides, in one aspect, a method for determining a physical property of a liquid sample, i.e., a test fluid, such as a viscometric and/or rheological property as well as a structural physical property such as gelation and/or crystallization, which employs an extended range rotating viscometer technique comprising: providing a suitable rotary viscometer with a rotor and a stator and having a suitably strong head, preferably a Brookfield-type viscometer, which includes a motor driving a rotor, a stator in which the test fluid is to be contained, with the rotor being driven in the test fluid in the stator, and a temperature-control feature which can control the temperature of the test fluid in the stator during testing; providing the test fluid to the stator, and immersing the rotor in the test fluid in the stator; rotatably contacting the rotor with the sample in the stator by driving the rotor immersed in the test fluid with the motor, typically under high shear stress conditions, while varying temperature of the temperature-control feature, and hence, the test fluid, as a function of time. Advantageously, the temperature is varied over a period of about half a day or less, for Third Zone correlations, and slower cooling (e.g. one degree Celsius per hour or less) for First Zone correlations, with temperature being lowered throughout the testing from and to a suitably low value; monitoring the stress and/or viscosity of the test fluid during the testing by measuring drag on the rotating rotor; and obtaining data therefrom. Also provided is a rotary viscometer device useful for carrying out the method.
The invention is useful in materials characterization, and especially in determining lubrication characteristics. In particular, it is useful to determine and predict lubricant characteristics in the xe2x80x9cFirst and Third Zones.xe2x80x9d
Significantly, the invention is a breakthrough in the field, particularly with respect to modem engine oil testing. Hereby, improvements in kind are provided the art for dramatically better characterizations of higher viscosity liquids and of the liquids as when classical structural characteristics such as gelation or crystallization develop. In particular, the invention makes it possible to characterize and compare such liquids and differentiate the effects of additive systems to control gelation and crystallization. Notably, with this invention, the differences of additive treatments to better disperse soot and to prevent soot-agglomeration as well as of oxidation inhibitors to prevent oxidation of the oil from causing low temperature pumpability problems can be determined. For the first time in the art, a relatively quick, highly efficient and reliable test method is made available to determine and predict engine oil performance in the newly recognized, critical region of performance from the oil pump to the lubrication site. Data pertinent to these xe2x80x9cFirst and Third Zonesxe2x80x9d is now found to be so necessary in evaluating oils and other liquid lubricants for performance in modem engines in temperate zone winter and arctic environments By this invention, accuracy, precision, rapidity, and repeatability heretofore unknown, as well as data heretofore inaccessible or unknown, is provided to the art in the test fluids of interest.
Surprisingly, sensitivity is satisfactory if not actually increased in the highly viscous or gelating liquid samples by employing the higher strength heads in the practice of the invention. This is contrary to that wisdom which had been believed or propounded by those ordinarily skilled or even expert in the art in that a rotary viscometer head having a high torque or a sensitivity of greater than seventy Pascals (Pa) would be ineffective in determining viscosity.
Numerous further advantages attend the invention.